If you've ever noticed that your dog can't lift one side of its face, or that one of its eyes seems to be drooping, he may have facial nerve paralysis. Facial paralysis in dogs is a condition caused by a malfunction of the facial nerve (cranial nerve VII), which controls the muscles that form facial expressions. Facial nerve paralysis in dogs can have many different causes, and this article will discuss them along with the treatment options.
What is the facial nerve in dogs and what are its functions?
The facial nerve is the seventh cranial nerve (CN VII), and it's responsible for the movement of the facial muscles. One of its branches also innervates part of the digastric muscle which is used for opening the mouth. It also controls the secretion of tears, and it's involved in the sense of taste. The facial nerve begins at the brainstem and runs through the middle ear before exiting the skull.
The pathology of the facial nerve can cause the muscles around the ear, eyes, nose, cheeks, and lips to become weak or paralyzed.
What are the causes of facial paralysis in dogs?
An idiopathic form of the disease (similar to Bell’s palsy in people) is the most common cause in dogs (up to 75%) and can also occur in cats. Other potential causes include extracranial causes (e.g. otitis media, otitis interna, head trauma, surgery of ear and face), metabolic disorders, peripheral inflammation, neurotoxins, and facial nerve neoplasia. Intracranial causes include inflammation and brainstem neoplasia.
Dogs are more commonly affected by idiopathic facial nerve paralysis, which is similar to Bell's palsy in people. Up to 75% of cases can be traced back to this cause. There are many other potential causes of facial paralysis in dogs. Some include infections or trauma outside of the head, metabolic disorders, problems with the peripheral nervous system, neurotoxins, and brain tumors. The following is a list of possible other possible reasons based on the underlying illness:
Infection: Infection of the inner or middle ear can cause facial nerve paralysis in dogs. Otitis interna or otitis media can cause facial nerve paralysis in 50% of dogs affected.
Inflammation and immune-mediated disease: Inflammation anywhere along the neurologic pathway can result in facial paralysis in dogs. Myasthenia gravis is an example.
Traumatic injury: Common examples would be bite wounds and head trauma.
Metabolic and endocrine disorders: These diseases are characterized by facial nerve (CN VII) dysfunction as a part of a whole systemic disease. Examples include hypothyroidism and Cushing's disease.
Neoplasia: Sometimes tumors can grow on the facial nerve or the brainstem and affect how it works. This can be because the tumor directly invades or compresses the nerve.
Neurotoxins: Botulism and tick paralysis can cause dysfunction to the facial nerve and result in facial nerve paralysis in dogs.
What are the symptoms of facial paralysis in dogs?
Acute signs of facial paralysis may include drooping ears and lips, excessive salivation, and inability to blink or retain food in the mouth. Symptoms of facial nerve paralysis typically only affect one side of the face. If it affects the nerve signals to your tear glands then you can develop keratoconjunctivitis sicca (KCS) which is tears leaving one's eyes so they dry out. You may also experience corneal ulceration if there are problems with your blink reflex and not enough tears are produced.
If the lesion is located in the middle ear, you may see signs of Horners syndrome, because nerves that control facial movement travel through this area. If a middle ear lesion extends into the inner ear, you may see problems with balance on the affected side. Balance problems or vestibular disease can also be seen in dogs with idiopathic disease.
How is facial paralysis in dogs diagnosed?
Clinical signs and cranial nerve reflex testing help diagnose the condition. Idiopathic facial paralysis can only be diagnosed after all known causes have been ruled out. Facial nerve paralysis in dogs is usually only one-sided or unilateral.
A thorough history and physical examination are key in the diagnostic process. A complete ophthalmic examination should be performed to rule out facial nerve lesions that present with similar symptoms (e.g. corneal ulceration, Horner syndrome).
An otoscopic examination of both ears is important to rule out otitis media or interna as a cause. While the middle and inner ear cannot be evaluated on an otoscopic examination, a ruptured eardrum (tympanic membrane) raises the suspicion. A neurologic examination should also be performed to look for any deficits in facial movement and other cranial nerve functions. Your veterinarian should perform blood work to help identify any metabolic or endocrine disorders that may be causing facial nerve paralysis.
Imaging of the head, specifically magnetic resonance imaging (MRI), may be important to help rule out any mass lesions or inflammation that may be causing facial nerve paralysis.
Treatment of facial paralysis in dogs
No definitive treatment exists for the paralysis itself and the treatment will depend on the underlying cause. Lubricating the eye every 4-6 hours to protect the cornea is recommended, especially if the blink response is absent.
Can a dog recover from facial paralysis?
The prognosis depends on the cause. If idiopathic facial paralysis is the underlying cause, improvement can occur over several weeks to months in some dogs. Recovery can be partial or complete. Studies have shown that 1/3 of dogs diagnosed with facial paralysis made a complete recovery within 3 years.
If the facial nerve function does not return, permanent contracture may develop as a consequence of chronic paralysis and scarring. Contracture may be confused for healing since the muscles no longer droop or sag. Contracture is when the muscles get very tight and don't function normally.
This article discussed facial paralysis in dogs and the different causes of it. It also goes over the symptoms and how it is diagnosed. The treatment options vary depending on the underlying cause but usually involve lubricating the eyes and providing general supportive care. The prognosis for dogs with facial paralysis varies depending on the cause but is usually favorable. Idiopathic facial paralysis can often result in a full or partial recovery. If you notice sudden symptoms of facial drooping in your dog, please contact your veterinarian for further advice.